Staff: Mentor

A microcontroller would not have the necessary transistors for this project? If it's possible that I don't need a relay then how would I close a switch?

You need to tell us more about what the switch is doing, in order for us to know how big it is. A microcontroller (uC) does not generally have much current source/sink capability ( a few mA, typically), so you cannot drive a regular (even small) relay directly. But there are other kinds of switch mechanisms that can be driven with very little current.

What voltages and currents will your switch experience? What is it a switch for?

It's an adaptive switch for controlling wheelchairs and other types of things. It is a very simple mechanical switch with a miniplug (like a stereo mini plug) at the end of a cable that connects to an adaptive device. Here is an example: http://www.infogrip.com/product_view.asp?RecordNumber=165&sbcolor=%23990033&option=switch&subcategory=&CatTxt=&optiontxt=Switch [Broken] I'm trying to figure out how I would interface my microcontroller to such a switch. A purely electronic switch would sound like a better idea but I'm not sure if it can interface with the adaptive device.

Staff: Mentor

It's an adaptive switch for controlling wheelchairs and other types of things. It is a very simple mechanical switch with a miniplug (like a stereo mini plug) at the end of a cable that connects to an adaptive device. Here is an example: http://www.infogrip.com/product_view.asp?RecordNumber=165&sbcolor=%23990033&option=switch&subcategory=&CatTxt=&optiontxt=Switch [Broken] I'm trying to figure out how I would interface my microcontroller to such a switch. A purely electronic switch would sound like a better idea but I'm not sure if it can interface with the adaptive device.

Oh, maybe we're misunderstanding your question. That's in input device, not an actuator. Do you want to monitor the switch with your uC? Or you somehow want to mechanically actuate that big thing?

If you want to click that switch somehow from your uC, you'll definitely need some power gain over the digital output control signal from your uC. Something like a solenoid actuator...

But, if you can put your circuit in parallel with the switch, you could have the uC close its own switch, which would imitate the pushbutton switch being actuated. Do you know what voltages and currents are involved with the circuit that the switch plugs into? Is your uC sharing the same ground as whatever circuit the switch plugs into, or do you need galvanic isolation.

BTW, working on wheelchair electronics is not trivial. I hope you know how important reliability of control and fail-safe operation are. Do you have 3 uCs voting?